This invention relates to optical fibers and, more particularly, to methods and apparatus for communicating optical signals between an optical fiber and a receiver or transmitter, such as a semiconductor receiver or transmitter mounted in a package.
Integrated circuit devices (ICs), such as microprocessors, micro controllers, and signal processors, are operating at higher and higher frequencies. For example, computer processors are currently being clocked at speeds in excess of 1 Gigahertz (GHz). At least two technological developments have contributed to this increase in operating speeds. Switching transistors, which are the building blocks of computers, now operate at lower voltages. For example, IC operating voltages have systematically dropped from 5.0 Volts to 2.2 Volts and below. Because switching power losses in transistors are proportional to the square of the operating voltage, the lower voltages reduce power dissipation, allowing higher frequency switching on the same substrate for the same total power dissipation. The second development is the use of sophisticated xe2x80x9cradio frequencyxe2x80x9d modeling techniques for designing the layouts of conductive leads. The leads can be modeled as high frequency transmission lines, and coupling between adjacent leads as well as discontinuities, such as bends, taken into account. Such modeling has allowed the design of high-performance, multi-layered PC boards.
Unfortunately, there are disadvantages associated with such advances, such as increased sensitivity to electromagnetic interference (EMI), to voltage transients, and to common-mode noise. Desired signals can be degraded. Creative engineering and sophisticated board layouts can help reduce the deleterious effects described above. However, limits still remain. It is understood that conductive leads to high speed, low voltage ICs simply create certain problems with signal integrity and limit the speed at which signals can be propagated. For example, designers of high-speed microprocessor boards restrict communication buses emanating from the microprocessor IC to approximately 300 MHz. Multiple, parallel 300 MHz buses are used to communicate with the IC at the full bandwidth of which the IC is capable, such as 1 GHz. Each bus carries only a part of the communication with the IC. Each bus, of course, has sensitivity to EMI and other influences that reduce the integrity of the transmitted signal.
Optical fibers are known to be highly desirable for the transmission of data and other signals. Optical fibers are low cost, flexible, have a large bandwidth, and are not sensitive to EMI. However, optical fibers are not widely adopted for the communication data to and from an IC, such as the microprocessor in a personal computer.
Basically, problems associated with launching signals onto the fiber or retrieving signals off of the fiber, or, in other words, communicating with the optical fiber, limit the use of optical fibers in environments such as a personal computer, despite the advantages of fiber in terms of bandwidth, flexibility and reduced sensitivity to EMI. Many of the known techniques for communicating with an optical fiber are simply too expensive compared to other technologies, such as the use of multiple conductive 300 MHz buses.
For example, in communicating an optical signal using a fiber, optical alignment of the fiber with the transmitter or receiver with which the fiber communicates is very important, especially in higher power and/or long haul applications, to ensure that light is efficiently transferred between the receiver or transmitter and the fiber. Optical fibers have very small dimensions, and often very tight tolerances must be achieved and maintained over a range of operating parameters, such as temperature, vibration, and humidity, to provide proper optical alignment.
One approach is to terminate optical fibers in precision connectors and to mate the connectors. However, an optical connector, such as a plug connector, is typically complex and includes multiple parts, some of which can be spring loaded. The connector maintains contact between the mated fiber faces when the plug is connected with a similarly highly engineered discrete socket, or jack. Plug and jack optical connectors can also require meticulous cleaning and are subject to all manner of degradation of the face of the fiber, including degradation due to micro-cracking, and due to foreign object damage caused by triboelectric charge forces attracting and holding small particles on the end face of the fiber prior to connection. The lowest cost multimode product known today, although injection molded and known for its lowest selling price, cannot be field terminated. It must be prepared in advance to a predetermined length, and in addition, is restricted to duplex applications.
Furthermore, fibers are typically too fragile without a protective coating, or buffering, to survive in real world applications. For example, an optical fiber is coated to prevent water ingression, which can lead to catastrophic failure due to water induced microcrack propagation. Typically, the fiber is coated with a polymer or polymers. In some cases the coating is applied in eight or more individual steps to protect the fiber from such failure. The most common protective coating is an ultra violet (UV) cured acrylate. Other coatings including fluoroacrylates, polyimides, Teflon fluoropolymers, and a number of other organic compounds.
Unfortunately, problems are associated with these protective coatings. The core of the fiber is often unpredictably located with respect to the outer circumference of the coating, hindering proper optical alignment for communication of light with the fiber.
Accordingly, the protective coating is often stripped away from a short length of the optical fiber prior to assembly of the length of fiber into a connector or optical package. The fiber is often mechanically stripped, which can damage the surface of the fiber and render the fiber more likely to fail in service. The fiber can also be stripped using hot sulfuric acid. However, the acid can degrade the fiber, including any remaining coatings, due to the wicking of the acid underneath one or more of the coatings. Stripping the fiber introduces a discontinuity in the protective coating where the coating suddenly ends and the stripped portion of the fiber begins. This discontinuity can concentrate stresses on the fiber at the discontinuity, also tending to promote failure of the fiber. The amount of stress concentrated can depend on the nature of the coating that is stripped.
It is also known to metallize, typically via electroplating, electroless plating, or vapor deposition, the cladding layer that is exposed upon stripping the fiber. The metallized cladding can be soldered into a ferrule, which ferrule is in turn soldered into a passage in an active or passive component package. xe2x80x9cGlues,xe2x80x9d such as epoxy resins, and RTV silicone compounds are used to fill in gaps and to avoid microbend induced stresses that cause unacceptable optical performance degradation. To enhance the mechanical integrity of the optical assembly, a part of the fiber in the ferrule may retain the polymer layer, such that the core of the optical fiber may be displaced relative to and/or disposed at an angle to the longitudinal axis of the ferrule. Often the length of the passage is longer than the length of the ferrule, and because of the high variability in fiber thickness due to unpredictable thickness and/or location of the protective coating, as noted above, the passage includes a large diameter. This creates the larger gap to fill with the xe2x80x9cgluexe2x80x9d and also increases the risk of angular misalignment of the fiber.
After all of the foregoingxe2x80x94stripping, plating, and soldering a ferrule onto the fiber and into a packagexe2x80x94it is typically still necessary for a technician to optically align the fiber and the device, that is, the receiver or transmitter in the package, with which the fiber communicates. Typically, the location of the packaged device or of a free end of the fiber is adjusted while measuring the transmission of light between the fiber and the device. When the location is found that corresponds to acceptable light transmission, the location of the device or the free end is fixed. In one common practice, a second ferrule is soldered to the fiber near the free end, and this ferrule is secured to the package by placing a clamp over the ferrule and welding the clamp to the package, thereby fixing the fiber in proper optical alignment with the device. This procedure is laborious and costly.
From the foregoing, it is apparent that improvement in methods and apparatus for communicating signals with an optical fiber would represent a welcome advance in the art. Accordingly, it is an object of the present invention to address one or more of the foregoing disadvantages or drawbacks of the prior art.
Other objects will become apparent below to one of ordinary skill in the art.
According to a preferred embodiment, an optical assembly for the communication of an optical signal between an optical fiber and a receiver or transmitter includes a body including a guideway and a first semiconductor optical element for conversion between electrical and optical signals and for receiving or transmitting light. The semiconductor optical element is mounted in register with the body. The optical assembly also includes an optical fiber having a first end, a core, a cladding surrounding the core, and a protective coating deposited on the cladding. The guideway receives a selected length of the optical fiber, where the selected length includes the entire length of the fiber received by the guideway. The selected length has not been stripped of a coating deposited on the cladding. When the selected length is received by the guideway, the first end of the optical fiber is optically aligned with the optical element such that neither the location of the first end nor the location of the optical element is adjusted responsive to the measurement of the transmission of light between the optical element and the optical fiber.
In another aspect of the invention, an optical apparatus includes a body including a guideway and a first semiconductor optical element for conversion between electrical and optical signals and for receiving or transmitting light. The semiconductor optical element is mounted in register with the body. The apparatus also includes an optical fiber, where the optical fiber extends from a first end to a second end and includes a core, a cladding surrounding the core, and a protective coating surrounding the cladding. The guideway receives a selected length of the optical fiber, and the protective coating is included on the fiber for at least a majority of the selected length. The selected length includes the entire length of the fiber received by the guideway. The optical fiber, when received by the guideway, has the first end optically aligned with the optical element such that neither the location of the first end nor the location of the optical element is adjusted responsive to the measurement of the transmission of light between the optical element and the optical fiber. The optical apparatus also includes a second guideway that receives a second selected length of the optical fiber, where the second selected length includes the entire length of the fiber received by the second guideway, and a second optical element that is optically aligned with the second end of the optical fiber. The protective coating is present along all of a length of the fiber, the length including the majority of the first selected length and a majority of the second selected lengths and the entire length of the optical fiber therebetween.
In yet a further aspect of the invention, an optical assembly for communication of an optical signal between an optical fiber and a receiver or transmitter includes a body including a guideway having a wall and a first semiconductor optical element for conversion between electrical and optical signals and for receiving or transmitting light. The semiconductor optical element is mounted in register with the body. The optical assembly also includes a length of optical fiber having a first end, a core, a cladding surrounding the core, and a coating deposited on the cladding. No other coating is deposited over the coating for the length of the fiber, and the coating has a thickness of less than about 1 micron. The length of optical fiber has an n-factor of at least 50. The guideway receives a selected length of the optical fiber such that the coating contacts the wall of the guideway, and the selected length includes the entire length of the fiber received by the guideway. The fiber includes the coating thereon for at least a majority of the selected length. The first end of the optical fiber is optically aligned with the optical element.
The invention also includes methods for communicating an optical signal between an optical fiber and a receiver or transmitter. In a preferred embodiment, the method includes providing a body; providing the body with a guideway; providing a semiconductor optical element for conversion between electrical and optical signals and for one of receiving and transmitting light; mounting the optical element in register with the body; providing an optical fiber having a first end, the optical fiber including a core, a cladding surrounding the core, and a hermetic coating deposited on the cladding; placing a selected length of the optical fiber in the guideway for being received thereby and for optically aligning the first end of the fiber with the optical element, the selected length being all of that portion of the optical fiber that is received by the guideway; refraining from stripping a coating in contact with the cladding from the selected length of the fiber; and wherein neither the location of the first end of the optical fiber nor the location of the optical element is adjusted responsive to the measurement of the transmission of light between the optical element and the optical fiber.